If the two media have really different densities, like air and water, then most of the energy is going to be reflected back, very little of it will keep going and get transmitted into the new medium.
而如果这两种介质的密度相差较大，就像空气和水那样，那么大部分的能量将会折射回来，只有一小部分会继续传播进入到新的介质中。
The researchers said, "An elder would be at risk of poorer diet to keep healthy."
研究人员说：“老人有吃更差的饮食，无法保持健康的风险。”
He should be able to keep his room tidy with the generous amount of storage space.
有大量的储物空间，他应该可以保持他房间的整洁。
Unless you are trying to lose weight to please yourself, it's going to be tough to keep your motivation level high.
除非你在为了让自己开心而努力减肥，否则要保持驱动力很高将很难。
If we don't keep bringing this to the attention of the people, nothing will be done.
如果我们无法让公众保持对此事的关注，那就将一事无成。
Voters can be remarkably forgiving of presidents who fail to keep their campaign promises.
选民们对于未能实现其竞选诺言的总统们能做到极其宽容。
There are fears that he will not be able to keep it up when he gets to the particularly demanding third year.
有人担心到了极其艰难的第3年他会坚持不下去的。
I felt it would be presuming on our personal relationship to keep asking her for help.
我觉得总要她帮忙就是利用了我们的私人交情。
You'll be told what rooms you can go into and what rooms you're to keep out of.
你会被告知哪些房间可以进入，哪些房间不能进入。
Be careful to keep your mouth in range of the microphone; don't weave around or turn away to answer a question from the side.
要注意保持你的嘴在麦克风的范围内；不要晃来晃去或转过身去回答旁边的问题。
Winemakers who still use cork but wish to keep production costs from rising will be forced to reconsider plastic stoppers.
那些仍在使用软木塞，但希望避免生产成本上升的酿酒师，将被迫重新考虑塑料塞子。
We need to be aware of the risks and keep working to alleviate the dangers.
我们需要意识到这些风险，并继续努力减轻这些危险。
If they fail, children should be encouraged to keep trying rather than to give up if they really want the desired result.
如果孩子们失败了，如果他们真的想要达成预期的成果，我们就应该鼓励他们继续努力，而不是让他们放弃。
If people like Kennedy are willing to keep it short to maximize their effectiveness as speakers, we should be smart enough to do the same thing.
如果像肯尼迪这样的人愿意保持演讲的简短以最大化他们作为演讲者的效力，我们也应该足够聪明做同样的事情。
Ekman's observation may be relevant to the British expression "keep a stiff upper lip" as a recommendation for handling stress.
埃克曼的观察结果可能与英国人的表达“保持冷静”有关，这是一种应对压力的建议。
While I was slow to accept that I would be the one to keep track of her shots, to schedule her vet appointments, to feed and clean her, Misty knew this on day one.
我慢慢才接受我可能是那个会拍照记录她的成长，带她看兽医，给她喂食，洗澡的人，但米斯蒂在第一天就知道了这一点。
Such stations will also be able to keep an eye on what is happening inside buildings, including offices.
这些监测站还将能够密切关注包括办公室在内的建筑物内发生的情况。
Someday we may be able to take any cell and keep it alive functioning and reproducing itself essentially forever through the use of telomerase.
总有一天，我们也许能够利用端粒酶使任何细胞保持活力，使其正常工作并永久地自我复制。
About 72% of "unretiree" respondents said that they would return to work once retired to keep mentally fit while 59% said it would be tied to making ends meet.
约72%的“不退休”受访者表示，他们一退休就会重返岗位，以保持心理健康；59%的受访者则表示这一选择与维持生计有关。
Because I'm writing my senior thesis, I'm supposed to be able to keep the book all semester.
我正在写毕业论文，所以我应该可以在整个学期保留这本书。
Grandmother will be able to keep warm and won't have to wear her shawl in bed.
奶奶就能保暖了，也不用在床上披披肩了。
Now, there are some cells that just seem to keep on dividing regardless, which may not always be a good thing if it gets out of control.
现在，有些细胞似乎不管怎样都在继续分裂，如果失去控制，这可能不是一件好事。
As transportation improved, distant and larger markets within the nation could be reached, thereby encouraging the development of larger factories to keep pace with increasing sales.
随着交通状况的改善，人们可以到达全国范围内更远更大的市场，从而鼓励更大型工厂的发展，以跟上销售增长的步伐。
As I start describing how quiet it is to be out in the woods, I keep mentioning how much effort it takes to keep going.
当我开始描述树林里面是多么安静时，我不断提及要花多少努力才能坚持下去。
Your pages will be easier to keep track of that way, and, if you have to clip a paragraph to place it elsewhere, you will not lose any writing on the other side.
这样做能让你的页面更加一目了然，并且，如果你必须剪切一个段落并把它放在其他位置上，另一侧的文字也不会丢失。
We can put the waxberry into wines, which is one traditional way to keep healthy and not be sick.
我们可以把杨梅放入酒中，这是一种保持健康、避免生病的传统方式。
You may be presenting complicated ideas or technical details but try to keep everything as simple as possible.
你可能也会展示一些很复杂的想法或一些技术细节，但请尽量一切从简。
If teachers keep it form-free and student-led, it can still be tied to a curriculum and an educational plan.
如果教师不拘泥于形式，以学生为主导，那么仍可以把它纳入学校课程和教育规划。
To be clear, people can't keep away from all the risks in this way, but it's the best choice.
需要明确的是，人们不能以这种方式远离所有的风险，但这是最好的选择。
To be honest, I never meant to keep my being a crime writer a secret or anything, and my friends have always known.
说实话，我从来没有想过要把我作为犯罪小说作家的身份保密，我的朋友们一直都知道这一点。
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